Traditional riding mowers, e.g., those typically having four wheels wherein the front wheels are conventionally steerable, are in common use by homeowners and professionals alike. However, for lawns having numerous obstacles, tight spaces, and/or intricate borders, riding mowers having zero-radius-turning (ZRT) capability are often preferred. As the name implies, “ZRT” generally indicates a vehicle having a very tight minimum turning radius, i.e., a vehicle that is highly maneuverable.
Most ZRT riding mowers have one or more drive wheels located on each side of the mower. The drive wheels are independently powered, e.g., by hydraulic motors or integrated zero-turn transaxles, so that, while a drive wheel on a first side of the mower may rotate in a first direction at a first speed, the drive wheel on the opposite side may rotate in the same or different direction at the same or different speed. Rotating one drive wheel for forward motion while simultaneously slowing, stopping, or reversing rotation of the drive wheel on the opposite side, causes the mower to turn. At the extreme, the mower may spin generally about a vertical axis located between the respective drive wheels.
Each drive wheel is typically coupled to a drive shaft or axle of a mower with a hub. The hub may include a flange having a conventional lug pattern to which the wheel attaches.
Often, the hub is attached to the drive axle with a coaxial fastener or mounting bolt and transfers rotational power through mating surfaces provided on both the axle and the hub. While this configuration is adequate for many applications, the frequent speed and direction changes common with ZRT mowers may cause the coaxial bolt to back out or loosen over time. This problem may be more apparent where the configuration of the hub and axle mating surfaces allows for greater rotational movement of the hub relative to the axle.
As a result, many ZRT mowers that utilize a central mounting bolt also utilize a hub/axle combination having relatively tight clearances, i.e., having minimal backlash or “looseness,” between the mating surfaces of the drive axle and the hub. Thus, relative motion between the axle and the hub is minimized, reducing the tendency for the mounting bolt to inadvertently loosen over time. Some configurations that provide such tight clearances include, for example, an axle and hub using a key and keyway to transfer torque. Other configurations may utilize a tapered axle and hub combination, where the axle transfers torque to the hub via the interference fit between the two components. Other options include permanently securing the hub to the axle, such as by welding. All these configurations provide minimal backlash and, thus, may be effective in limiting the loosening effect on the mounting bolt during mower operation.
While effective at reducing backlash, these hub and axle configurations are potentially expensive to produce. Although the cost may be acceptable for larger, commercial grade equipment, it may be economically undesirable for smaller mowers, e.g., those directed primarily to homeowners. Moreover, smaller ZRT mowers may not have a drive axle of sufficient diameter to accommodate the desired keyway or taper configuration.
Another technique known for preventing loosening between two components is lockwiring. While effective, lockwiring can be labor-intensive and require a certain level of skill to properly install. In addition, lockwire is usually destroyed upon removal, i.e., it is generally not reusable.